a) Field of the Invention
The present invention relates to apparatus and method for actively reducing a vibration. The present invention particularly relates to the actively vibration reducing apparatus and method in which a controlled vibration developed from a controlled vibration source is interfered against the vibration transmitted from a vibration (developing) source such as a vehicular engine toward a vibration source supporting base such as a vehicular body to reduce the vibration. The present invention, more particularly, relates to the actively vibration reducing apparatus and method in which in a control algorithm to derive the controlled vibration source, the control algorithm including a transfer function established between the controlled vibration source and a detector for detecting a residual vibration after the interference of the controlled vibration against the vibration, the transfer function can be calculated and identified in a very short period of time with a high accuracy without use of a processor capable of calculating and processing complicated calculation equations nor use of a high-capacity memory.
b) Description of the Related Art
In such an actively vibration reducing apparatus as described above, the transfer function between the controlled vibration source and residual vibration detector is minutely different for each product due to its characteristic deviation in an equipment to which the actively vibration reducing apparatus is applied or in an installation to which the actively vibration reducing apparatus is applied. In addition, the above-described transfer function tends to be varied from an originally set state thereof due to a characteristic variation in time along with a use of the actively vibration reducing apparatus in the applied equipment.
Hence, it is desirable to identify the transfer function after the actively vibration reducing apparatus has been incorporated into the applied apparatus or identify the transfer function for each regular checking performed for the applied apparatus in order to execute a vibration reduction control with the high accuracy.
A Japanese Patent Application First Publication No. Heisei 6-332471 published on Dec. 2, 1994 exemplifies a first previously proposed actively noise or vibration reducing apparatus in which the transfer function is identified.
In the first previously proposed actively (vibration or noise) reducing apparatus disclosed in the above-identified Japanese Patent Application First Publication, an identification sound or identification vibration is developed in accordance with an impulse signal from a controlled sound source or the controlled vibration source and its (impulse) response is measured by means of a residual sound detector or residual vibration detector so that the transfer function described above required in the control algorithm of the actively noise or vibration reducing apparatus is identified.
In addition, a timing at which the identification sound or identification vibration in accordance with the impulse signal is developed is limited to a time immediately before a state in which no noise or vibration is developed from a noise source or the vibration source is transferred to that in which it is developed. Hence, the identification of the transfer function can be performed without remarkable increase in a calculation load and without unpleasant feeling given to a listener or user in the identification sound or vibration environment.
Another Japanese Patent Application First Publication No. Heisei 3-259722 published on Nov. 19, 1991 exemplifies a second previously proposed noise reducing apparatus in which a noise developed by a compressor of a refrigerator and irradiated externally from a duct of a machine room is canceled before the noise is irradiated from the duct. In the second previously proposed actively noise reducing apparatus disclosed in the above-identified Japanese Patent Application First Publication, loud speaker and microphone are installed in the duct and a controlled sound is developed from the loud speaker according to a driven state of the microphone so as to carry out the noise reduction.
In addition, in order to prevent a noise control characteristic in the second previously proposed actively noise reducing apparatus from being deteriorated, the identification sound in accordance with a white noise is developed to measure a transfer function established between the loud speaker and the microphone so as to identify a digital filter in a controller of the second previously proposed noise reducing apparatus.